Product Documentation

Accepting Optimization Recommendations

Sep 15, 2014

Workload Balancing provides recommendations about ways you can migrate virtual machines to optimize your environment. Optimization recommendations appear in the WLB tab in XenCenter.



This illustration shows a screen capture of the Optimization Recommendations list, which appears on the WLB tab. The Reason column displays the purpose of the recommendation. The Operation column displays the behavior change suggested for that optimization recommendation. This screen capture shows an optimization recommendation for a virtual machine, HA-prot-VM-7, and a host, host17.domain4.bedford4.ctx4.

Basis for optimization recommendations

Optimization recommendations are based on the:

  • Placement strategy you select (that is, the placement optimization mode), as described in Adjusting the Optimization Mode
  • Performance metrics for resources such as a physical host's CPU, memory, and network utilization
  • The role of the host in the resource pool. When making placement recommendations, Workload Balancing considers only the pool master if no other host can accept the workload. (Likewise, when a pool is operating in Maximum Density mode, Workload Balancing considers the pool master last when determining the order in which to fill hosts with virtual machines.)

The optimization recommendations display the name of the virtual machine that Workload Balancing recommends relocating, the host it currently resides on, and the host Workload Balancing recommends as the machine's new location. The optimization recommendations also display the reason Workload Balancing recommends moving the virtual machine (for example, "CPU" to improve CPU utilization).

After you accept an optimization recommendation, XenServer relocates all virtual machines listed as recommended for optimization.

Tip: You can find out the optimization mode for a resource pool by selecting the pool in XenCenter and checking the Configuration section of the WLB tab.

To accept an optimization recommendation

  1. Select the pool for which you want to display recommendations in the Resources pane and then click on the WLB tab. If there are any recommended optimizations for any virtual machines on the selected resource pool, they display on the WLB tab.
  2. To accept the recommendations, click Apply Recommendations. XenServer begins moving all virtual machines listed in the Optimization Recommendations section to their recommended servers.

    After you click Apply Recommendations, you can click Notifications and then Events tab to display the progress of the virtual machine migration.

Understanding WLB recommendations under High Availability

If you have Workload Balancing and the XenServer High Availability feature enabled in the same pool, it is helpful to understand how the two features interact. Workload Balancing is designed not to interfere with High Availability. If there is a conflict between a Workload Balancing recommendation and a High Availability setting, the High Availability setting always takes precedence. In practice, this means:

  • Workload Balancing will not automatically power off any hosts beyond the number specified in the Failures allowed box in the Configure HA dialog.
    • However, Workload Balancing may still make recommendations to power off more hosts than the number of host failures to tolerate. (For example, Workload Balancing will still make a recommendation to power off two hosts when High Availability is only configured to tolerate one host failure.) However, when you attempt to apply the recommendation, XenCenter may display an error message stating that High Availability will no longer be guaranteed.
    • When Workload Balancing is running in automated mode and has power management enabled, any recommendations that exceed the number of host failures to tolerate are ignored. In this situation, if you look in the Workload Balancing log, you will see a message that says a power-management recommendation was not applied because High Availability is enabled.